In the foregoing list of diseases associated with specific bacteria,
attention has been drawn to the common modes of infection, or, as they
are technically called, “portals of entry,” and it now remains to touch
upon the main factors, processes, and results following upon the entry
into the body of such disease-producing microbes.
It is a well-known fact that the normal blood has of itself to a
considerable extent the power of killing germs which may wander into
it through various channels. Likewise the tissue cells of the body
in general show similar action depending upon the different cell
groups, state of health, general robustness, and period of life. The
germ-killing power varies in different individuals, though each may be
quite healthy. Considered as a whole, this power possessed by the body
against germs is known as “general resistance.” And when by any means
this power of resistance is lost or diminished, we run grave risks of
incurring disease.
Granted a case of infection, let us now trace up briefly what occurs.
Between the period when the bacteria gain a lodgment and that in which
the disease assumes a noticeable form, the patient simply feels out of
sorts. It is during this stage that the blood and tissues are deeply
engaged in the attempt to repel the attacks of the invading microbes.
With varying speed the germs multiply throughout the body generally,
or may be at first localized, or even, as in lockjaw, remain localized
throughout the entire disease. Multiplying in the tissues, they
generate in increasing amounts their noxious poisons, which soon cause
profound changes throughout the body; the patient becomes decidedly
ill, and shows now the signs of an unmistakable infection.
Does the body now give up the fight entirely? No; on the contrary, the
white blood-cells, the wandering cells, and the cells of the tissues
most affected still carry on an unequal fight. From the lymphatic
glands and spleen, armies of white cells rush to the fray and attempt
to eat up and destroy the foe, but possibly in vain; the disease runs
its course, to end either in death or recovery.
How, then, in cases of recovery, are the microbes finally overcome?
This question involves many complex processes which at present are by
no means thoroughly understood, but we will concern ourselves with the
simple principles.
It has been previously mentioned that once the bacteria get a good
foothold the body is subjected to the action of generated poisons,
which are known as toxins. They give rise to such symptoms as loss of
appetite, headache, fever, pains and aches, and even a state of stupor
or unconsciousness. In addition to the active warfare of the white
blood-cells, groups of cells throughout the body, after recovering from
the first rude shock of the toxins, begin to tolerate their presence,
then effect a change in the chemical constitution of the toxins, and
finally elaborate substances which antagonize the toxins and destroy
their action altogether, thus lending aid to the warrior cells, which
at last overcome the invading microbes. Recovery is brought about, and
a more or less permanent degree of immunity against the special form of
disease ensues.
Now if we could use these antagonizing substances, or, as they are
called, antitoxins, upon other men or animals sick with a similar
disease, would their bodies be at once strengthened to resist and
finally overcome the disease? Yes, in a certain majority of cases they
would, and this is exactly what scientific observers have noted,
worked out, and have successfully applied. A new art in the healing of
disease, which is spoken of broadly as serum-therapy, or medication by
curative or protective serums, has thus been discovered.
The first observers in this new field were Pasteur and Raynaud in
France in 1877–78, and Salmon and Smith in this country in 1886.
Raynaud, by injecting serum from a calf which had had an attack of
cow-pox, prevented the appearance of the disease in a calf freshly
inoculated with the virulent material of the disease. Pasteur, by using
feebly infective germs of fowl cholera, conferred immunity upon healthy
fowls against the disease, and was able to cure those which were ill.
Salmon and Smith injected small and repeated amounts of the elaborated
toxins or poisons of the bacillus of hog cholera into healthy swine,
and were able to confer immunity upon them.
However, it was not until Behring in 1892 announced his discovery of
an antitoxin serum for diphtheria, along with an undisputed proof of
its value in treatment, that the attention of the scientific world
was finally aroused and stimulated to the appreciation of the great
possibilities of serum-therapy.
Strange as it may seem, much opposition arose to this new method of
treatment, not alone from the lay portions of the community, but even
from the ranks of the medical profession itself. This opposition was
due in part to misconceptions of the principles involved in the new
doctrine, and in part to the falsely philanthropic prejudices of the
pseudo-scientific sections of both parties. But by the persevering work
of the enthusiastic believers in serum-therapy, positive conviction has
now replaced misconception and prejudice in the minds of the majority
of its former opponents.
The accumulation of statistical evidence, even where all allowance is
made for doubtful methods of compilation, shows that the aggregate
mortality of diphtheria has been reduced fully fifty per cent. since
the introduction of antitoxic treatment by Behring in 1892.
Since the method of preparation of the commercial diphtheria antitoxin
illustrates the general principles involved in the search for the
production of curative or protective serums for infectious diseases in
general, a summary of the steps in its manufacture will now be given.
A race of diphtheria bacilli, which has been found to yield a poison of
great virulence in alkaline beef broth, is grown for a week or ten days
in this medium. The toxin is then separated and its virulence exactly
determined. It is preserved in sterile receptacles for immediate or
future use. The next step is the inoculation of a suitable animal with
the toxin. Of all animals the horse has been found to meet nearly every
requirement. Such an animal, in a state of perfect health, receives
an injection of twenty cubic centimetres of toxin, along with ten
or fifteen of standard antitoxin, beneath the skin of the neck or
fore-quarters, upon three separate occasions at intervals of five days.
After this it receives increasing doses of toxin, alone, at intervals
of six to eight days, until, at the end of two months, it is able to
stand with little discomfort doses of such strength that if given in
the first stage these doses would have quickly caused death.
At this period the horse is bled to a small extent, and its serum
tested to ascertain if prospects are good for the production by the
animal of a high grade of antitoxin. If satisfactory progress has been
made, the injections are continued for another month, when, as a rule,
the maximal degree of antitoxic power in the serum will have been
attained.
The horse is now bled to the proper extent, the blood being received
in a sterile jar and placed in an ice-box. Here it coagulates, and
the serum separates from it. When the separation of clot and serum
is complete, the latter is drawn off, taken to the laboratory, and
standardized. This being finished, an antiseptic fluid is added to
preserve the serum from decomposition. It is then bottled, labelled,
and sent out for use.
In similar fashion tetanus antitoxin is prepared; and quite recently
Calmette has produced an antitoxic serum for use in snake bite, by
injecting horses with minute increasing doses of snake venom. His
experiments have given some remarkable results, not only in laboratory
work, but also in cases of actual snake bite occurring in man. Thus
bacteriological scientists, after years of laborious work, in the face
of much criticism and severe denunciation, may confidently announce
that they have in their possession a magic key to one of nature’s
secret doors. The lock has been turned. The door stands partly open,
and we are permitted a glimpse of the future possibilities to be
attained in the great fight against disease.